Method for the detection of subcutanous cardiac signals and a cardiac device for use in detecting subcutaneous cardiac signals

Abstract

A cardiac device and method for detecting QRS signals within a composite heart signal of a body including providing at least two input heart signals via at least two separate input channels, wherein each of the at least two input heart signals is recorded by pairs of sensing electrodes that have one electrode in common and provided coincidental in time. The cardiac device and method include generating estimated signals from the input heart signals, combining the input heart signals and the estimated signals to a combined input stream (SECG), and detecting the QRS signal by comparing the combined input stream (SECG) to an adaptive detection threshold (ATHR) which adapts throughout time.

What is claimed is: 
     
       1. A method for the detection of QRS signals, comprising:
 providing at least two input heart signals via at least two separate input channels, wherein each channel is connected to pairs of external sensing electrodes, and wherein the at least two input heart signals are recorded by said pairs of external sensing electrodes and provided coincidental in time; 
 generating estimated signals from the at least two input heart signals;
 wherein the estimated signals are one or more of at least one spatially derived estimate and at least one temporally derived estimate; 
 
 combining the estimated signals to a combined input stream (SECG); and, 
 detecting a QRS signal by comparing the combined input stream (SECG) to an adaptive detection threshold (ATHR) which adapts throughout time. 
 
     
     
       2. The method according to  claim 1 , wherein the at least one temporally derived estimate for an input channel of said at least two separate input channels comprises a smoothed value calculated from samples of the at least two input heart signals of said input channel. 
     
     
       3. The method according to  claim 1 , wherein the at least one spatially derived estimate of an input channel of said at least two separate input channels is calculated as a combination of the at least two input heart signals provided by at least a second input channel of said at least two separate input channels. 
     
     
       4. The method according to  claim 2 , wherein the step of combining the estimated signals to a combined input stream (SECG) comprises combining the at least one spatially derived estimate, the at least one temporally derived estimate and the input heart signal of an input channel for each input channel of said at least two separate input channels respectively, to provide a composite estimate signal for each input channel of said at least two separate input channels respectively. 
     
     
       5. The method according to  claim 4 , wherein the step of combining the estimated signals to a combined input stream (SECG) further comprises
 calculating a prospect for each of the at least two separate input channels respectively, using the composite estimate signals, wherein within the calculation of a certain prospect for a channel, the respective composite estimate signal calculated for the respective channel is augmented; and, 
 choosing at least one prospect as the combined input stream (SECG). 
 
     
     
       6. The method according to  claim 1 , wherein the adaptive detection threshold (ATHR) is set after each detection of a QRS signal, wherein the value of the adaptive detection threshold (ATHR) is initially set as a percentage of a QRS-peak amplitude of the combined input stream (SECG) measured during a detection of a QRS signal, and wherein the adaptive detection threshold (ATHR) decreases throughout time. 
     
     
       7. The method according to  claim 6 , wherein the adaptive detection threshold (ATHR) decreases in steps (S) until it reaches a target threshold (TT), wherein the duration of a step (S) is adjusted based on a moving average of the ventricular cycle length measured from a composed heart signal of a body from which the combined input stream (SECG) is measured. 
     
     
       8. The method according to  claim 7 , wherein the value of the target threshold (TT) is initially set as a percentage of a QRS-peak amplitude of the combined input stream (SECG) measured during a detection of a QRS signal, and wherein the adaptive detection threshold (ATHR) and the target threshold (TT) are always greater than or equal to a minimum threshold (LAT). 
     
     
       9. The method according to  claim 4 , wherein the minimum threshold (LAT) is determined by the composite estimate signals, and wherein a vector residual of the composite estimate signals is used to determine the minimum threshold (LAT). 
     
     
       10. The method according to  claim 7 , wherein a low signal flag (LSF) is set if a detected QRS-peak amplitude of the combined input stream (SECG) is lower than a scaled value of the minimum threshold (LAT). 
     
     
       11. The method according to  claim 1 , wherein one electrode of the pairs of external sensing electrodes is shared by two of the at least two separate input channels. 
     
     
       12. A cardiac device ( 100 ) for use in detecting QRS signals within a composite heart signal of a body, comprising:
 an input unit ( 10 ) configured to provide at least two input heart signals via at least two separate input channels, wherein each channel is connected to pairs of external sensing electrodes, and wherein at least two input heart signals are recorded by said pairs of external sensing electrodes and provided coincidental in time; 
 an estimation unit ( 20 ) configured to generate estimated signals from the at least two input heart signals; 
 a combination unit configured to combine the estimated signals to a combined input stream (SECG); 
 an automatic sensor control unit ( 50 ) configured compare the combined input stream (SECG) to an adaptive detection threshold (ATHR) which adapts throughout time to detect a QRS signal; and, 
 a system adjustment unit ( 60 ) configured to adjust at least one parameter of le automatic sense control unit ( 50 ). 
 
     
     
       13. The cardiac device ( 100 ) according to  claim 12 , further comprising:
 at least one filter unit configured to filter one or more of the at least two input heart signals and the combined input stream (SECG). 
 
     
     
       14. The cardiac device according to  claim 12 , wherein one electrode of the pairs of external sensing electrodes is configured to be shared by two of the input channels. 
     
     
       15. A method for the detection of QRS signals, comprising:
 providing at least two input heart signals via at least two separate input channels, wherein each channel is connected to pairs of external sensing electrodes, and wherein the at least two input heart signals are recorded by said pairs of external sensing electrodes and provided coincidental in time; 
 generating estimated signals from the at least two input heart signals; 
 combining the estimated signals to a combined input stream (SECG); and, 
 detecting a QRS signal by comparing the combined input stream (SECG) to an adaptive detection threshold (ATHR) which adapts throughout time; 
 wherein the adaptive detection threshold (ATHR) is set after each detection of a QRS signal, wherein the value of the adaptive detection threshold (ATHR) is initially set as a percentage of a QRS-peak amplitude of the combined input stream (SECG) measured during a detection of a QRS signal, and wherein the adaptive detection threshold (ATHR) decreases throughout time. 
 
     
     
       16. The method according to  claim 15 , wherein the adaptive detection threshold (ATHR) decreases in steps (S) until it reaches a target threshold (TT), wherein the duration of a step (S) is adjusted based on a moving average of the ventricular cycle length measured from a composed heart signal of a body from which the combined input stream (SECG) is measured. 
     
     
       17. The method according to  claim 16 , wherein the value of the target threshold (TT) is initially set as a percentage of a QRS-peak amplitude of the combined input stream (SECG) measured during a detection of a QRS signal, and wherein the adaptive detection threshold (ATHR) and the target threshold (TT) are always greater than or equal to a minimum threshold (LAT). 
     
     
       18. The method according to  claim 16 , wherein a low signal flag (LSF) is set if a detected QRS-peak amplitude of the combined input stream (SECG) is lower than a scaled value of the minimum threshold (LAT). 
     
     
       19. The method according to  claim 15 , wherein one electrode of the pairs of external sensing electrodes is shared by two of the at least two separate input channels. 
     
     
       20. A cardiac device ( 100 ) for use in detecting QRS signals within a composite heart signal of a body, comprising:
 an input unit ( 10 ) configured to provide at least two input heart signals via at least two separate input channels, wherein each channel is connected to pairs of external sensing electrodes, and wherein at least two input heart signals are recorded by said pairs of external sensing electrodes and provided coincidental in time; 
 an estimation unit ( 20 ) configured to generate estimated signals from the at least two input heart signals; 
 a combination unit configured to combine the estimated signals to a combined input stream (SECG); and, 
 an automatic sensor control unit ( 50 ) configured compare the combined input stream (SECG) to an adaptive detection threshold (ATHR) which adapts throughout time to detect a QRS signal. 
 
     
     
       21. The cardiac device ( 100 ) according to  claim 20 , further comprising:
 at least one filter unit configured to filter one or more of the at least two input heart signals and the combined input stream (SECG). 
 
     
     
       22. The cardiac device according to  claim 20 , wherein one electrode of the pairs of external sensing electrodes is configured to be shared by two of the input channels.